Magnetic compositions containing iron, rhodium, and selected elements from groups ii-, iii-a, iv-a, v-a and vi-a



United States Patent O a corporation of Delaware No Drawing. Filed May 3, 1962, Ser. No. 192,059 8 Claims. (Cl. 75-122) This invention relates to, and has as its principal object provision of, new magnetic materials useful for the interconversion and control of various forms of energy.

Magnetic materials, inclusive of both ferroand ferrimagnetic materials, are broadly old and many such compositions are known. Similarly, many energy transducer devices based thereon are also known. However, the previously known ferromagnetic compositions suffered variously from one or more inferior properties, qualities, or behavior. For instance, many of the ferromagnetic compositions did not exhibit as high saturation magnetization values as was desired for many outlets, nor did they exhibit sufiicient corrosion, oxidation, or high temperature resistance. While some of these ferro-, ferrimagnetic compositions did exhibit the rather, peculiar property of an abrupt and large-scale increase in saturation mag netization with increasing temperature, those previously known either exhibited this so-called exchange inversion temperature at relatively low temperature and/ or suffered from having too low a Curie temperature for successful application in many desired embodiments.

The iron/ rhodium binary alloys of, for instance, Fallot, Revue Scientifique, 77, 498 (1939), and Kouvel et al., General Electric Research Report No. 61-RL-2870M, November 1961, also exhibited this abrupt increase in saturation magnetization with increasing temperature with aa' of about 112 gauss cm.- /g., i.e., 112 emu/g, as measured in a 5,000 oersteds (or conventionally a 5 koe.) magnetic field, but at a temperature of only 350 K. (i.e., about 77 C.). Furthermore, the temperature at which the material suddenly changes from antiferromagnetic to ferromagnetic could not be widely varied without increasing greatly the ratio of residual magnetization to maximum magnetization.

There has now been discovered a new class of ferromagnetic materials which exhibit very good saturation magnetization values and high Curie temperatures. These compositions are also outstanding in corrosion and oxidation resistance and thermal degradation, properties in which many or most of the presently known magnetic compositions are found wanting. These new magnetic materials exhibit a maximum saturation magnetization within a restricted temperature range and a very much smaller saturation magnetization at temperatures above and below this range. These magnetic compositions exhibit a relatively low saturation magnetization at low temperatures which abruptly increases with increasing temperature, at a specific temperature range for each composition, to a maximum saturation magnetization many orders of magnitude greater than that exhibited at tem peratures below this critical temperature range. This maximum saturation magnetization slowly decreases with increasing temperature until the Curie temperature is reached. On being cooled from the Curie temperature these preferred compositions exhibit slowly increasing magnetization with decreasing temperature until a maximum saturation magnetization value is reached and then abruptly exhibit a large decrease in saturation magnetization, reaching utlimately a low remanence saturation magnetization. The maximum saturation magnetization is generally the same on decreasing temperature as that 3,144,324 Patented Aug. 11, 1964 achieved on increasing temperature. However, the temperature at which the maximum value is exhibited is somewhat lower on a decreasing temperature cycle than an increasing temperature cycle, i.e., there is magnetization hysteresis as a function of cycling temperature. These products are also very hard.

Devices for the interconversion and control of various forms of energy based on this preferred class of magnetic compositions comprise another portion of the present invention. Another preferred embodiment of the invention is directed to methods for preparing these preferred magnetic products exhibiting these novel magnetic properties, and also to the preparation of energy transducers broadly based on such products.

These superior magnetic compositions consist essentially of iron and rhodium in major proportion and at least one A-Group element selected from the group beryllium, magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, and tellurium, i.e., a member of Group II-A of the Periodic Table of the elements of atomic ice . number 4 to 12 or a member of Groups III-A, IV-A,

V-A, VI-A of the Periodic Table of the elements of atomic number 13 through 83, inclusive. The iron and rhodium will normally be present in substantially equal atomic proportions, but not necessarily equal since either may exceed the other by 20 atomic percent. It is always necessary that both iron and rhodium be present. At least one other metal selected from the list beryllium magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, and tellurium, which also must always be present, will range in amount from 0.01-0.20 atom proportions. Thus, the new superior magnetic compositions of the present invention are alloys of the formula wherein M represents an A-Group metal selected from the list beryllium, magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium, and tellurium, x is an integer from one to six and generally one to two, a and b, which can be alike or different, are numbers ranging from 0.8-1.2, and c is a number ranging from 0.010.20, and in the instance when x22, the requisite cs can be alike or different but still must fall in the indicated range. These subscript numbers refer to the atomic proportions of the modified elements in the final alloy. M can be different within the same defined group when x is greater t an 1.

The following examples in which the parts given are by weight are submitted to illustrate the present invention further and not to limit it.

parts of rhodium, and 0.0741 part of antimony, all in finely divided form, was placed in a die and pressed into 60 la pellet. The pellet was dropped into an aluminum oxide crucible which was then placed inside the heating element of a carbon-resistance furnace. A bell jar was placed over the furnace which was then evacuated and heated to approximately 800 C. Argon was admitted into the bell jar until the pressure in the furnace was 0.5 atmosphere. The temperature of the furnace was then increased until the metal pellet had visibly melted (about 1600 C.) The metal pellet was held in the molten state for five minutes, after which the temperature was gradually reduced over a period of ten minutes at which time the furnace was turned off at an approximately internal itemperature of 300 C. The crucible was removed from the furnace, and the 48Fe/50Rh/2Sb. (atom percent) alloy slug removed. The metallic-appearing product was strongly attracted by a magnet at room temperature but was only very weakly attracted after cooling below C.

To guarantee homogeneity, the metal slug was sealed in an evacuated silica tube and heated at 950 C. for 41 hours, after which it was cooled slowly to room tempera ture over a period of 36 hours. After this annealing treatment, the slug superficially and physically appeared unchanged. Below '.10 C., it had a residual magnetization of 4 emu/g. On warming above this temperature, it underwent a rapid and large-scale change in saturation magnetization and exhibited a maximum at 64 C. of 100 emu/ g. Its Curie temperature was 405 C.

For brevity, the additional detailed examples illus trative of the present invention are covered in the following table in which these new magnetic compositions were prepared as described in full detail in Example I in the foregoing with the indicated variations in charge composition, preparation temperature, time required to reduce furnace temperature to permit removal of the charge, and, finally, the annealing time and the resultant different magnetic properties. As in Example I, in all instances the charge was held in the molten state at the indicated preparative temperature for five minutes. In this table the charged compositions are indicated in atomic percent. The annealing temperature was, in all instances, at 950 C., and the symbol T refers to the temperature at which the indicated new magnetic composition undergoes the rapid and large-scale change in saturation magnetization upon heating. The symbol T is used to represent the Curie temperature. The symbol o is used to indicate the residual magnetization of the sample. The symbol a is used to indicate the maximum saturation magnetization of the material, and the column headed temp-5 indicates the temperature at which this maximum saturation magnetization value is attained. In all instances in all columns involving temperature the units are in C. The saturation magnetization data were obtained using a magnetic field of 15.75-

4 minor amount of the so defined A-Group metals, but is also inclusive of thise alloycompositions consisting essentially of Fe and Rh in major amount and relatively minor amounts of more than one of the so defined A- Group elements. Thus, the present invention is also specifically inclusive of four, five, six, seven, eight, etc., element-containing alloys wherein the Fe and Rh are always present and in major amount, and the other A-Group elements as listed above are present in minor amount. Thus, to be specific, the presentinvention also includes the following multicomponent magnetic alloys:

and the like.

The novel compositions of the present invention may exhibit a maximum saturation magnetization at temperatures in the range 269 C. to +37S C. and Curie temperatures in the range +300 to +500 C. The magnetic compositions also exhibit increasing saturation magnetization with increasing temperature in a temperature range below the Curie point.

Such compositions are useful in devices operating at temperatures near room temperature and even at elevated temperature for those exhibiting maximum saturation magnetizations in the higher temperature ranges. Those exhibiting maximum saturation magnetization at very low temperatures are especially useful in devices such as refrigerators and temperature-sensitive controls operating at temperatures near the boiling point of liquid helium and below. The manner in which saturation magnetization varies with temperatures can be controlled by modifying the composition of the ferromagnetic products. The

most outstanding compositions exhibit a very low residual magnetism below the lower ferromagnetic transistion temperature.

These novel magnetic compositions are prepared by 16.00 koe. (i.e., kiloersteds or 15,750l6,000 oersteds). heatmg mixtures of the elements or compounds of the ele- Table I Time to '1? Composition Prep Reduce Anneal (heat- To me as... T

Temp. Temp, Time, ing

min. hrs.

48 Fe/50Rh/2 Mg 1,075 10 24 55 435 4 97 100 4a Fe/50 Rh/2 Al 1, 550 13 39 438 7 102 134 48 Fe/50 Rh/2 Ga 1, 500 10 39 10 43s 3 104 87 4s Fe/50 Rh/2 $1-. 1,800 10 41 5a 435 2 104 150 48 Fe/60 1111 2 Ge. 1, 650 15 24 62 415 2 107 93 lie/ Rh/5 Sb 1, 560 10 26 22 320 2 53 170 48 Fe/48 Rh 4 Sb- 1, 495 10 29 145 42s 30 106 5 50 Fe 4s 311/2 Sb 1,495 10 29 -100 460 24 115 25 4s Fe/50 Rl1/2 s 1,400 10 41 0 432 1 s7 s3 1 Prereacted FeS used as a source of sulfur.

Suitable specific compositions within the scope of the present invention, i.e., those materials consisting essentially of Fe, Rh, and at least one A-Group element selected from the list beryllium, magnesium, aluminum, gallium, indium, silicon, germanium, tin, lead, phosphorus, arsenic, antimony, bismuth, sulfur, selenium and ,tellurium include ments to a temperature in the range from 600 to 2500" C., or higher, as equipment and vapor pressure limitations dictate within the normal practice. Temperatures of 700 to 850 C. and from 1200 to 1800 C. are usually employed. Temperatures of at least about 1400-1700 C. are generally necessary if the compositions are to be melted. The time of heating is'not critical but should be sufficient to permit complete reaction of the ingredients. Heating times ranging up to about 50 hours for the lower temperatures ranges are necessary to elfect appreciable solid state reaction. Longer times can be useful in some cases, particularly, for instance, if it is desired to prepare reactiohin inert refractory materials under reduced pressure or under a protective blanket of an inert gas.

The materials employed in preparing these new compositions can be the elements themselves or any of the binary or ternary combinations thereof as called for by the desired stoichiometry; Thus, to prepare Fe/Rh/Ga the three elements themselves can be charged or the necessar y'Fe/ Rh binary can be separately prepared previously and then mixed with the requisite amount of Ga and re- ;action effected to form the desired ternary composition. In any event, it is preferred that the materials be in powder or granulated form and that they be well mixed before heating is commenced.

The starting materials are employed in such relative amounts that the resulting mixture contains the desired proportions of Fe/Rh and the requisite A-Group metal. Thus, to prepare an Fe /Rh /Sb ternary, the respective elements or binaries are charged in the indicated relative atomic proportions.

After the desired preparative heating cycle has been completed, the reaction mixture is cooled and this first cooling cycle will be relatively rapid.

T o assure the greatest homogeneity in the product and the maximum ferromagnetic behavior, it has been found that the products should preferably be annealed by holding for a relatively long time at an elevated temperature and then slowly cooling to room temperature over a controlled temperature profile, e.g., by a suitably programed recorder-driven furnace. Thus, it is preferred that the products of the present invention after the preparative heating and cooling cycle, whether or not any intervening mechanical, chemical, or magnetic purification is effected, be heated to an elevated temperature in the range 800.1000 .C. or higher and held at tln's temperature for relatively long periods of time, e.g., from 24 to 100 hours or so, in an inert atmosphere, i.e., under evacuated conditions or with a protective blanket of an inert gas such as argon or helium. Then, the compositions of the present invention are further annealed carefully by final slow cooling from this temperature to room temperature over a period of approximately 24 hours.

The novel magnetic compositions of this invention eX- hibit several magnetic characteristics which make them especially valuable for use in various specific applications. The novel lower ferromagnetic transition temperature is a distinguishing feature conferring unusual utility on these materials. Particularly outstanding are the relatively high saturation magnetization values exhibited by these compositions, as well as the high Curie temperature and good values of saturation magnetization exhibited at the maximum with increasing temperature below the Curie temperature. All the compositions are resistant to corrosion, oxidation, and exhibit good magnetic behavior at elevated temperatures.

The preferred products are useful in devices for the interconversion and control of various forms of energy such as solar motors, temperature-sensitive inductors, thermally activated clutches, and temperature compensators in devices based on conventional magnetic material where sagging of magnetic properties with increasing temperature is functionally deleterious. In their essential features all of these devices comprise at least three components, viz., the magnetic component described previously, suitable means for applying a form of energy to and from the magnetic component, and suitable means for utilizing the output from the magnetic component. For some applications, the devices of the present invention can include means for controllably magnetizing and demanetizing the magnetic component. 'At temperatures within the ferromagnetic range, these compositions can be used in any of the conventional applications for ferromagnetic materials for which their properties render them suitable, e.g., electromagnets, high-frequency coil cores, information and memory storage elements, and the like.

In the preferred devices the elements which provide heat to or remove heat from the magnetic element, which magnetize and demagnetize the magnetic element, and which collect and detect the new form of energy produced are conventional in the art. For example, by introducing a pivotal element, with a magnetic component as just described, in a magnetic field and having means for magnetizing the magnetic component, the pivotal element can be caused to move in said field. In this way, mechanical work can be done. The pivotal element can be an armature, an oscillating arm, or a metering device.

The preferred compositions of the present invention are useful as the active component in forming temperature responsive electrical inductors comprising, usually in combination, a metallic core consisting at least in part of one of the present magnetic compositions with or without a second material exhibiting a magnetic permeability which is substantially invariant with temperature, and an electrical conductor wrapped around said core. These temperature responsive electrical (magnetic) inductors are widely useful in any circuits in which inductance is a significant parameter. Thus, these inductors based on the present magnetic compositions can be employed as an element of the frequency-determining circuit of a sinewave oscillator or as a high-temperature safety device to reduce circuit current with increasing temperature or as a current-controlling device in which the control 'current flows through a heater winding on the temperature-sensitive inductor. In addition, these temperature-responsive inductors can be used in conjunction with a wide variety of conventional core materials, including both the metallic and oxide types, representative of which latter are, for example, the ferrites.

In view of the increasing saturation magnetization with increasing temperature below the Curie temperature, the preferred materials of the present invention are useful in forming temperature responsive magnetically operated rotary force couplings comprising, in combination, a pair of relatively rotatable elements to be coupled disposed adja cent to one another in a common magnetic flux path, a

permanent magnet, and one of the new magnetic compositions of the present invention which exhibits a changing permeability accompanying a reversible first order transition from a first solid state phase to a second solid state phase at a given temperature, both disposed in said common magnetic flux path, the permanent magnet and the magnetic composition of the present invention completing a magnetic flux circuit between the said elements of the pair coupling one of the elements with the other in that temperature range when the magnetic composition of the present invention exists in a first solid state phase and uncoupling the elements of the pair as the temperature decreases when the substance exists in a second solid state phase, and obviously the reverse and in cycles.

The preferred compositions of the present invention are also useful in thermomagnetic devices as the working substance therein, said devices being useful for efiecting heat transfer, i.e., serving as heat pumps, e.g., a refrigerator. These new magnetic compositions in such devices in view of the first order solid phase to solid phase transition with changing temperature with accompanying relatively large change in internal energy content in going through the transition will function as the said working substance in said devices with allied coupled magnetic means for cyclically inducing said transition in a direction such as to lower the temperature of the substance when one solid state phase is attained and to increase the temperature when the other solid state phase is attained, along with an allied heat source and a thermal sink relative to one of the solid state phases individually adapted to effect heat transfer sequentially With respect to said substance.

With respect to the thermomagnetic working capability of the preferred compositions, they are of particular interest in the formation of gradient objects comprising the said magnetic materials varying in composition angularly about a point or axis or varied along one or more selected lines, which need not be straight, in the said gradient object such as to display the first order solid phase to solid phase transition at successively higher temperatures in a first path or a direction along or about said point or axis 'of said line, and at successively lower temperatures in an opposite path or direction achieved by varying the composition of the magnetic alloys. These gradient objects are particularly useful in many kinds of energy-converting devices, e.g., as temperature indicators, cores in temperature-sensitive inductors, transformers, elements in thermal switches, and the like, and are particularly outstanding because of the possible ready and precise adjustment of device operation achievable to suit particular environmental conditions obtained with the great control possible through the narrow compositional changes.

These preferred materials are also useful as the working substance in a method of information storage and retrieval wherein a recording member containing one of the new magnetic compositions of this invention substantially homogeneously distributed therethrough is exposed to a read-in beam, modulated patternwise in accordance with information to be stored from a temperature variation inducing component, thereby establishing in the said recording member regions of relatively higher and relatively lower intrinsic magnetization corresponding to said information, maintaining said element after said read-in at a temperature within the thermal hysteresis range, and reading out the stored information by exposing the element at said temperature to a low intensity electron beam whereby deviations in said beam corresponding to the stored information are produced and converted into electrical signals. Intrinsic magnetization is used here as defined by Cusack, The Electrical and Magnetic Properties of Solids, LongmansFGreen & Company, London, 1958, page 315.

The first order solid phase to solid phase transition accompanied by thermal hysteresis which is exhibited by the preferred materials is characterized by abrupt change not only in the magnetic properties but also in a number of the other physical properties of the material and any of these properties can be employed in any sensing or read-out method. Thus, after modulated read-in, read-out can be based on the change in electrical resistance of the new magnetic materials serving as the working substance of said recording member simply by providing read-out means sensitive to changes in resistance. Alternatively, read-out can be based upon changes in a linear dimension or in a volume of the working substance as desired.

Because of their outstanding magnetic properties coupled with good stability to temperature, atmosphere, corrosion, oxidation, and the like, and particularly because of the relatively high Curie temperatures that they possess,

the preferred magnetic materials are broadly outstanding as the working substances in various devices whereby, generically, magnetic energy is changed controllably to mechanical, electrical, or thermal energies; mechanical energy is converted controllably into electrical, magnetic, or thermal energies; or thermal energy is .controllably converted to mechanical, magnetic, or electrical energies.

More specifically, the preferred compositions of the present invention can serve as the working substances in magnetic switches, radiation-intensity meters, reciprocating engines, devices for maintaining constant temperature difference between two zones, magnetic balances, thermomagnetic generators, solar motors, temperature indicators, image-forming components, magnetic flashers, variable resistors, differential transformers, temperature responsive resonators, and the like.

Since obvious modifications and equivalents in the invention will be evident to those skilled in the chemical arts, I propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An alloy composed of (A) iron, (B) rhodium, and (C) at least one member of the group consisting of elements of Group II-A of the Periodic Table of atomic number 4-12 and elements of Groups III-A, IV-A, V-A and VI-A of atomic number 13-83 in the atom proportions of 0.8-1.2 of (A), 0.8-1.2 of (B), and 0.01-0.20 of (C).

2. An alloy of claim 1 in which (C) is antimony.

. An alloy of claim 1 in which (C) is magnesium.

. An alloy of claim 1 in which (C) is aluminum. An alloy of claim 1 in which (C) is gallium.

. An alloy of claim 1 in which (C) is silicon.

. An alloy of claim 1 in which (C) is germanium.

. An alloy of claim 1 in which (C) is sulfur.

No references cited. 

1. AN ALLOY COMPOSED OF (A) IRON, (B) RHODIUM, AND (C) AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF ELEMENTS OF GROUP II-A OF THE PERIODIC TABLE OF ATOMIC NUMBER 4-12 AND ELEMENTS OF GROUPS III-A, IV-A, V-A AND VI-A OF ATOMIC NUMBER 13-83 IN THE ATOM PROPORTIONS OF 0.8-1.2 OF (A), 0.8-1.2 OF (B), AND 0.01-0.20, OF (C). 